Efficacy of oral irinotecan against neuroblastoma xenografts

Liposomal Irinotecan Shows a Larger Therapeutic Index than Non-liposomal Irinotecan in Patient-Derived Xenograft Models of Pancreatic Cancer

INTRODUCTION

Liposomal irinotecan promotes controlled sustained release of irinotecan (CPT-11), therefore, we hypothesize that the therapeutic index (quantitative measurement of the relative efficacy/safety ratio of a drug) will be higher for liposomal than non-liposomal irinotecan.

METHODS

We compared the therapeutic indexes of liposomal and non-liposomal irinotecan in mice bearing subcutaneous patient-derived xenograft (PDX) pancreatic tumors under dosing regimens approximating the clinical setting. Following preliminary drug sensitivity/antitumor activity analyses on three PDX tumor models, one model was selected for analyses of efficacy, biomarker, toxicology, pharmacokinetics in mice receiving liposomal irinotecan (2.5, 10, 50 mg/kg/week) or non-liposomal irinotecan (10, 25, 50 mg/kg/week). The maximum tolerated dose (MTD) for each treatment was 50 mg/kg/week.

RESULTS

Using the selected IM-PAN-001 model at the MTD (both treatments, 50 mg/kg/week), antitumor activity, phospho-histone gamma-H2AX protein staining in cancer cell nuclei, histological tumor regression, and plasma levels of CPT-11 and its active metabolite SN-38 after 24 h were greater with liposomal than non-liposomal irinotecan, but tumor SN-38 levels were similar. At the lowest doses assessed, antitumor activity, histological tumor regression, and jejunum and bone marrow toxicity were similar. Based on these findings, liposomal and non-liposomal irinotecan had therapeutic indexes of 20 and 5, respectively.

CONCLUSION

This non-clinical study showed a fourfold broader therapeutic index with liposomal than non-liposomal irinotecan in mice bearing IM-PAN-001 PDX pancreatic tumors, even at optimal dosing for the two drugs. These findings support the clinical benefit observed with liposomal irinotecan in patients with pancreatic cancer.

CPT11 with P-glycoprotein/CYP 3A4 dual-function inhibitor by self-nanoemulsifying nanoemulsion combined with gastroretentive technology to enhance the oral bioavailability and therapeutic efficacy against pancreatic adenocarcinomas

Therapeutic efficacies of orally administrated hydrophobic chemodrugs are decreased by poor water solubilities and reduced oral bioavailabilities by P-glycoprotein (P-gp) and CYP450. In this study, CPT11 alone or combined with dual-function inhibitors (baicalein (BA) silymarin (SM), glycyrrhizic acid (GA), and glycyrrhetinic acid (GLA)) of P-gp and CYP450 loaded in a lecithin-based self-nanoemulsifying nanoemulsion preconcentrate (LBSNENP) to improve the solubility and inhibit the elimination by P-gp and CYP450. Results revealed that the LBSNENP composed of Capryol 90, lecithin/Tween 80/Cremophor EL, and propylene glycol at a weight ratio of 18:58:24 (designated PC90C10P0) was optimally selected. Encapsulating CPT11 with PEO-7000K in PC90C10P10/30 further enhanced the resultant hydrogel to be gastro-retainable and to release CPT11 in a sustained manner. Pharmacokinetic study of CPT11-loaded PC90C10P0 administered orally revealed an absolute bioavailability (FAB, vs. intravenous CPT11) of 7.8 ± 1.01% and a relative bioavailability (FRB1, vs. oral solution of CPT11) of 70.7 ± 8.6% with a longer half-life (T_1/2) and mean residence time (MRT). Among the dual-function inhibitors, SM was shown to be the most influential in increasing the oral bioavailability of CPT11. SM also increased the plasma concentration of the SN-38 active metabolite, which formed from the enhanced plasma concentration of CPT11. It is concluded that treatment with CPT11 loaded in PC90C10P0 with or without solubilization with SM could expose tumors to higher plasma concentrations of both CPT11 and SN-38 leading to enhancement of tumor growth inhibition with no signs of adverse effects.

Nanoparticle delivery of an SN38 conjugate is more effective than irinotecan in a mouse model of neuroblastoma

Neuroblastoma (NB) is the most common and deadly solid tumor in children. The majority of NB patients have advanced stage disease with poor prognosis, so more effective, less toxic therapy is needed. We developed a novel nanocarrier-based strategy for tumor-targeted delivery of a prodrug of SN38, the active metabolite of irinotecan. We formulated ultrasmall-sized (<100 nm) biodegradable poly(lactide)-poly(ethylene glycol) based nanoparticles (NPs) containing SN38 conjugated to tocopherol succinate (SN38-TS). Alternative dosing schedules of SN38-TS NPs were compared to irinotecan. Comparison of SN38-TS NPs (2 doses) with irinotecan (20 doses) showed equivalent efficacy but no cures. Comparison of SN38-TS NPs (8, 8, and 16 doses, respectively) to irinotecan (40 doses) showed that all SN38-TS NP regimens were far superior to irinotecan, and "cures" were obtained in all NP arms. SN38-TS NP delivery resulted in 200× the amount of SN38 in NB tumors at 4 hr post-treatment, compared to SN38 detected for the irinotecan arm; no toxicity was seen with NPs. We conclude that this SN38-TS NP formulation improved delivery, retention, and efficacy, without causing systemic toxicity.

TrkB inhibition by GNF-4256 slows growth and enhances chemotherapeutic efficacy in neuroblastoma xenografts

PURPOSE

Neuroblastoma (NB) is one of the most common and deadly pediatric solid tumors. NB is characterized by clinical heterogeneity, from spontaneous regression to relentless progression despite intensive multimodality therapy. There is compelling evidence that members of the tropomyosin receptor kinase (Trk) family play important roles in these disparate clinical behaviors. Indeed, TrkB and its ligand, brain-derived neurotrophic factor (BDNF), are expressed in 50-60 % of high-risk NBs. The BDNF/TrkB autocrine pathway enhances survival, invasion, metastasis, angiogenesis and drug resistance.

METHODS

We tested a novel pan-Trk inhibitor, GNF-4256 (Genomics Institute of the Novartis Research Foundation), in vitro and in vivo in a nu/nu athymic xenograft mouse model to determine its efficacy in inhibiting the growth of TrkB-expressing human NB cells (SY5Y-TrkB). Additionally, we assessed the ability of GNF-4256 to enhance NB cell growth inhibition in vitro and in vivo, when combined with conventional chemotherapeutic agents, irinotecan and temozolomide (Irino-TMZ).

RESULTS

GNF-4256 inhibits TrkB phosphorylation and the in vitro growth of TrkB-expressing NBs in a dose-dependent manner, with an IC₅₀ around 7 and 50 nM, respectively. Furthermore, GNF-4256 inhibits the growth of NB xenografts as a single agent (p < 0.0001 for mice treated at 40 or 100 mg/kg BID, compared to controls), and it significantly enhances the antitumor efficacy of irinotecan plus temozolomide (Irino-TMZ, p < 0.0071 compared to Irino-TMZ alone).

CONCLUSIONS

Our data suggest that GNF-4256 is a potent and specific Trk inhibitor capable of significantly slowing SY5Y-TrkB growth, both in vitro and in vivo. More importantly, the addition of GNF-4256 significantly enhanced the antitumor efficacy of Irino-TMZ, as measured by in vitro and in vivo growth inhibition and increased event-free survival in a mouse xenograft model, without additional toxicity. These data strongly suggest that inhibition of TrkB with GNF-4256 can enhance the efficacy of current chemotherapeutic treatment for recurrent/refractory high-risk NBs with minimal or no additional toxicity.

A phase II window study of irinotecan (CPT-11) in high risk Ewing sarcoma: a Euro-E.W.I.N.G. study

BACKGROUND

The prognosis for patients with nonpulmonary metastatic Ewing sarcoma remains poor with survival in the order of 15-20%. The need to introduce effective new agents into clinical practice is clear. Based on a preclinical rationale of responses in xenografts and backed by a phase I study in children, the Euro-E.W.I.N.G consortium planned a phase II window study of irinotecan in newly diagnosed high risk metastatic patients with Ewing sarcoma.

PROCEDURES

Patients were recruited between April 2004 and December 2007. Two courses of irinotecan were administered at a dose of 600 mg/m(2) as a 1 hour infusion at 21 day intervals. Response evaluation was determined after the second course of treatment by radiological assessment of primary and metastatic sites and, where appropriate bone marrow sampling.

RESULTS

Twenty-three patients were recruited. Two patients were deemed inevaluable for response. Five patients (24%) demonstrated a partial response. Grade 3 or 4 diarrhoea was seen in 4/43 course of treatment and was managed with loperamide.

CONCLUSIONS

This is the first report of single agent irinotecan activity in an untreated population of patients with Ewing sarcoma. In common with other paediatric tumours and other camptothecin analogues such as topotecan, single agent activity is only modest. The exact role for the use of irinotecan in patients with ES, dose schedule and combinations with other agents still requires further investigation.

Current and future strategies for relapsed neuroblastoma: challenges on the road to precision therapy

More than half of the patients with high-risk neuroblastoma (NB) will relapse despite intensive multimodal therapy, with an additional 10% to 20% refractory to induction chemotherapy. Management of these patients is challenging, given disease heterogeneity, resistance, and organ toxicity including poor hematological reserve. This review will discuss the current treatment options and consider novel therapies on the horizon. Cytotoxic chemotherapy regimens for relapse and refractory NB typically center on the use of the camptothecins, topotecan and irinotecan, in combination with agents such as cyclophosphamide and temozolomide, with objective responses but poor long-term survival. I-meta-iodobenzylguanidine therapy is also effective for relapsed patients with meta-iodobenzylguanidine-avid disease, with objective responses in a third of cases. Immunotherapy with anti-GD2 has recently been incorporated into upfront therapy, but its role in the relapse setting remains uncertain, especially for patients with bulky disease. Future cell-based immunotherapies and other approaches may be able to overcome this limitation. Finally, many novel molecularly targeted agents are in development, some of which show specific promise for NB. Successful incorporation of these agents will require combinations with conventional cytotoxic chemotherapies, as well as the development of predictive biomarkers, to ultimately personalize approaches to patients with "targetable" molecular abnormalities.

Tumor dosimetry using [124I]m-iodobenzylguanidine microPET/CT for [131I]m-iodobenzylguanidine treatment of neuroblastoma in a murine xenograft model

PURPOSE

[(124)I]m-iodobenzylguanidine ((124)I-mIBG) provides a quantitative tool for pretherapy tumor imaging and dosimetry when performed before [(131)I]m-iodobenzylguanidine ((131)I-mIBG) targeted radionuclide therapy of neuroblastoma. (124)I (T (1/2) = 4.2 days) has a comparable half-life to that of (131)I (T (1/2) = 8.02 days) and can be imaged by positron emission tomography (PET) for accurate quantification of the radiotracer distribution. We estimated expected radiation dose in tumors from (131)I-mIBG therapy using (124)I-mIBG microPET/CT imaging data in a murine xenograft model of neuroblastoma transduced to express high levels of the human norepinephrine transporter (hNET).

PROCEDURES

In order to enhance mIBG uptake for in vivo imaging and therapy, NB 1691-luciferase (NB1691) human neuroblastoma cells were engineered to express high levels of hNET protein by lentiviral transduction (NB1691-hNET). Both NB1691 and NB1691-hNET cells were implanted subcutaneously and into renal capsules in athymic mice. (124)I-mIBG (4.2-6.5 MBq) was administered intravenously for microPET/CT imaging at 5 time points over 95 h (0.5, 3-5, 24, 48, and 93-95 h median time points). In vivo biodistribution data in normal organs, tumors, and whole-body were collected from reconstructed PET images corrected for photon attenuation using the CT-based attenuation map. Organ and tumor dosimetry were determined for (124)I-mIBG. Dose estimates for (131)I-mIBG were made, assuming the same in vivo biodistribution as (124)I-mIBG.

RESULTS

All NB1691-hNET tumors had significant uptake and retention of (124)I-mIBG, whereas unmodified NB1691 tumors did not demonstrate quantifiable mIBG uptake in vivo, despite in vitro uptake. (124)I-mIBG with microPET/CT provided an accurate three-dimensional tool for estimating the radiation dose that would be delivered with (131)I-mIBG therapy. For example, in our model system, we estimated that the administration of (131)I-mIBG in the range of 52.8-206 MBq would deliver 20 Gy to tumors.

CONCLUSIONS

The overexpression of hNET was found to be critical for (124)I-mIBG uptake and retention in vivo. The quantitative (124)I-mIBG PET/CT is a promising new tool to predict tumor radiation doses with (131)I-mIBG therapy of neuroblastoma. This methodology may be applied to tumor dosimetry of (131)I-mIBG therapy in human subjects using (124)I-mIBG pretherapy PET/CT data.

Pre-Clinical Evaluation of rHDL Encapsulated Retinoids for the Treatment of Neuroblastoma

Despite major advances in pediatric cancer research, there has been only modest progress in the survival of children with high risk neuroblastoma (NB) (HRNB). The long term survival rates of HRNB in the United States are still only 30-50%. Due to resistance that often develops during therapy, development of new effective strategies is essential to improve the survival and overcome the tendency of HRNB patients to relapse subsequent to initial treatment. Current chemotherapy regimens also have a serious limitation due to off target toxicity. In the present work, we evaluated the potential application of reconstituted high density lipoprotein (rHDL) containing fenretinide (FR) nanoparticles as a novel approach to current NB therapeutics. The characterization and stability studies of rHDL-FR nanoparticles showed small size (<40 nm) and high encapsulation efficiency. The cytotoxicity studies of free FR vs. rHDL/FR toward the NB cell lines SK-N-SH and SMS-KCNR showed 2.8- and 2-fold lower IC50 values for the rHDL encapsulated FR vs. free FR. More importantly, the IC50 value for retinal pigment epithelial cells (ARPE-19), a recipient of off target toxicity during FR therapy, was over 40 times higher for the rHDL/FR as compared to that of free FR. The overall improvement in in vitro selective therapeutic efficiency was thus about 100-fold upon encapsulation of the drug into the rHDL nanoparticles. These studies support the potential value of this novel drug delivery platform for treating pediatric cancers in general, and NB in particular.

A single-arm pilot phase II study of gefitinib and irinotecan in children with newly diagnosed high-risk neuroblastoma

BACKGROUND

Gefitinib potently inhibits neuroblastoma proliferation in vitro, and the gefitinib/irinotecan combination shows greater than additive activity against neuroblastoma xenografts. This Phase II pilot study estimated the rate of response to two courses of intravenous irinotecan plus oral gefitinib in children with untreated high-risk neuroblastoma.

METHODS

Two courses of irinotecan [15 mg/m(2)/day (daily ×5)×2] were combined with 12 daily doses of gefitinib (112.5 mg/m(2)/day). Response was assessed after 6 weeks. A response rate >55% was sought.

RESULTS

Of the 23 children enrolled, 19 were evaluable for response. Median age at diagnosis was 3.1 years (range, 18 days-12.7 years). Most patients were older than 24 months (n = 20; 87%), male (n = 18; 78%), white (n = 16; 70%), had INSS 4 disease (n = 19; 83%), and had adrenal primary tumors (n = 18; 78%); nine patients (39%) had amplified tumor MYCN. The toxicity of gefitinib/irinotecan was mild and reversible (nausea, 5/20; diarrhea, 8/20; vomiting, 7/20). Five patients had partial responses; 9 others had a 23%-60% decrease in primary tumor volume and/or improved MIBG scans or decreased bone or bone marrow tumor burden. Median (range) systemic irinotecan exposure (AUC) was 283 ng/ml*hr (range, 163-890 ng/ml*hr) and 28 ng/ml*hr (3.6-297 ng/ml*hr) for the active metabolite, SN-38. No relation was observed between response and tumor expression of EGFR, MRP2-4, ABCG2, and Pgp.

CONCLUSIONS

Although the gefitinib/irinotecan combination was very tolerable and induced responses, it was not sufficiently active to warrant further investigation. Initial investigational studies of this type can preclude the necessity for larger, longer, and costlier trials.

Extended phase I evaluation of vincristine, irinotecan, temozolomide, and antibiotic in children with refractory solid tumors

BACKGROUND

The combination of irinotecan, temozolomide, and vincristine is appealing because of potentially synergistic mechanisms of action and non-overlapping toxicities. This phase I study was designed to determine the toxicity and maximum tolerated dose (MTD) of escalating daily protracted doses of irinotecan given in this combination. With extended accrual, we more fully explored the toxicity of multiple courses at the MTD.

PROCEDURE

Patients under 22 years with recurrent or refractory solid tumors were eligible. A course of chemotherapy was given every 28 days. Cefpodoxime was given for diarrhea prophylaxis. Vincristine (1.5 mg/m2, max 2 mg) was given intravenously (IV) on days 1 and 8. Temozolomide (100 mg/m2/day) was given orally on days 1-5. Irinotecan was given IV over 1 hr on days 1-5 and 8-12. Dose escalation was done in the standard 3 + 3 cohort design, starting at 15 mg/m2/day.

RESULTS

Twenty-five of 26 eligible patients were evaluable for toxicity and response. They received 111 courses (1-13, median 4). Dose limiting toxicity (DLT-pancreatitis, transaminitis) was seen in two of three patients at dose level 2 (20 mg/m2). No patients at level 1 had DLT during the first two cycles. Thus, the MTD of irinotecan in this combination is 15 mg/m2/day x 10 doses. Hematologic toxicity was mild and not prolonged. Grade 3 diarrhea was seen in five courses. Responses included two complete and two partial with 12 stable disease (SD) (median 6 months).

CONCLUSIONS

This combination is safe and shows activity in pediatric patients with recurrent malignancy.

Phase I trial of oral irinotecan and temozolomide for children with relapsed high-risk neuroblastoma: a new approach to neuroblastoma therapy consortium study

PURPOSE

Irinotecan and temozolomide have single-agent activity and schedule-dependent synergy against neuroblastoma. Because protracted administration of intravenous irinotecan is costly and inconvenient, we sought to determine the maximum-tolerated dose (MTD) of oral irinotecan combined with temozolomide in children with recurrent/resistant high-risk neuroblastoma.

PATIENTS AND METHODS

Patients received oral temozolomide on days 1 through 5 combined with oral irinotecan on days 1 through 5 and 8 through 12 in 3-week courses. Daily oral cefixime was used to reduce irinotecan-associated diarrhea.

RESULTS

Fourteen assessable patients received 75 courses. Because neutropenia and thrombocytopenia were initially dose-limiting, temozolomide was reduced from 100 to 75 mg/m(2)/d for subsequent patients. Irinotecan was then escalated from 30 to 60 mg/m2/d. First-course grade 3 diarrhea was dose-limiting in one of six patients treated at the irinotecan MTD of 60 mg/m2/d. Other toxicities were mild and reversible. The median SN-38 lactone area under the plasma concentration versus time curve at this dose was 72 ng . hr/mL. One patient with bulky soft tissue disease had a complete response through six courses. Six additional patients received a median of seven courses (range, three to 22 courses) before progression.

CONCLUSION

This all-oral regimen was feasible and well tolerated in heavily pretreated children with resistant neuroblastoma, and seven (50%) of 14 assessable patients had response or disease stabilization for three or more courses in this phase I trial. SN-38 lactone exposures were similar to those reported with protracted intravenous irinotecan. The dosages recommended for further study in this patient population are temozolomide 75 mg/m2/d plus irinotecan 60 mg/m2/d when given with cefixime.

The pediatric preclinical testing program: description of models and early testing results

BACKGROUND

The Pediatric Preclinical Testing Program (PPTP) is an initiative supported by the National Cancer Institute (NCI) to identify novel therapeutic agents that may have significant activity against childhood cancers. The PPTP has established panels of childhood cancer xenografts and cell lines to be used for in vivo and in vitro testing. These include panels for Wilms tumor, sarcomas (rhabdomyosarcoma, Ewing sarcoma, and osteosarcoma), neuroblastoma, brain tumors (glioblastoma, ependymoma, and medulloblastoma), rhabdoid tumors (CNS and renal), and acute lymphoblastic leukemia (ALL). Here, we describe the characteristics of the in vivo tumor panels and report results for the in vivo evaluation of two standard agents, vincristine and cyclophosphamide.

PROCEDURES

Solid tumors were grown subcutaneously in immune-deficient mice and tumor dimensions were measured weekly. ALL xenografts were inoculated intravenously and human CD45-positive cells were enumerated weekly.

RESULTS

Vincristine-induced objective responses in 6 of 24 (25%) and cyclophosphamide-induced objective responses in 18 of 28 (64%) solid tumor models. Comparable assessments of high levels of activity for these two agents were obtained using a tumor growth delay (TGD) measure. Both agents induced regressions in each of the ALL models evaluated.

CONCLUSIONS

We have established 51 solid tumor and 10 ALL in vivo models. The models identify vincristine and cyclophosphamide as having broad-spectrum activity. The PPTP tumor panels appear to generally recapitulate the activity of these agents against specific childhood cancers and to have the potential for identifying novel agents having significant clinical activity.

Evaluation of ABT-751 against childhood cancer models in vivo

OBJECTIVE

ABT-751 is a novel antimitotic agent that binds tubulin at the colchicine binding site. ABT-751 is undergoing Phase I trials in children, but has not been evaluated against a range of pediatric tumor models in vivo.

MATERIALS AND METHODS

ABT-751 was evaluated against 27 subcutaneously implanted xenograft models of childhood cancer including neuroblastoma [4], osteosarcoma [4], Ewing sarcoma [2] rhabdomyosarcoma [8], medulloblastoma [1] and eight kidney cancer lines (six Wilms tumors, two rhabdoid). ABT-751 was administered at 100 mg/kg P.O. on a schedule of 5 days on, 5 days off, 5 days on, repeating the cycle at 21 days. Tumor diameters were measured at 7 day intervals for a period of 12 weeks. Three measures of antitumor activity were used: (1) clinical response criteria [e.g., partial response (PR), complete response (CR), etc.]; (2) treated to control (T/C) tumor volume at day 21; and (3) a time to event measure based on the median event free survival (EFS) of treated and control lines.

RESULTS

ABT-751 induced regression in 4 of 25 models (16%) including models of neuroblastoma that are refractory to vincristine and paclitaxel. Other regressions occurred in rhabdomyosarcoma and Wilms tumor models. ABT-751 significantly increased event free survival (EFS > 2.0) in eight models (33%) in addition to those with objective responses.

CONCLUSIONS

ABT-751 demonstrated intermediate activity against this tumor panel. Neuroblastoma models appear somewhat more sensitive to this agent, with objective regressions also in rhabdomyosarcoma and Wilms tumor. ABT-751 was also active in several tumor lines intrinsically refractory to vincristine or paclitaxel.

Irinotecan: a potential new chemotherapeutic agent for atypical or malignant meningiomas

Object

There is currently no effective chemotherapy for meningiomas. Although most meningiomas are treated surgically, atypical or malignant meningiomas and surgically inaccessible meningiomas may not be removed completely. The authors have investigated the effects of the topoisomerase I inhibitor irinotecan (CPT-11) on primary meningioma cultures and a malignant meningioma cell line in vitro and in vivo.

Methods

The effects of irinotecan on cellular proliferation in primary meningioma cultures and the IOMM-Lee malignant meningioma cell line were measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and flow cytometry. Apoptosis following drug treatment was evaluated by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and the DNA laddering assays. The effects of irinotecan in vivo on a meningioma model were determined with a subcutaneous murine tumor model using the IOMM-Lee cell line.

Irinotecan induced a dose-dependent antiproliferative effect with subsequent apoptosis in the primary meningioma cultures (at doses up to 100 μM) as well as in the IOMM-Lee human malignant meningioma cell line (at doses up to 20 μM) irinotecan. In the animal model, irinotecan treatment led to a statistically significant decrease in tumor growth that was accompanied by a decrease in Bcl-2 and survivin levels and an increase in apoptotic cell death.

Conclusions

Irinotecan demonstrated growth-inhibitory effects in meningiomas both in vitro and in vivo. Irinotecan was much more effective against the malignant meningioma cell line than against primary meningioma cultures. Therefore, this drug may have an important therapeutic role in the treatment of atypical or malignant meningiomas and should be evaluated further for this purpose.

Pleiotrophin, a candidate gene for poor tumor vasculature and in vivo neuroblastoma sensitivity to irinotecan

In vivo neuroblastoma (NB) xenograft model, resistant to the DNA-topoisomerase I inhibitor irinotecan (CPT-11), has been established to study resistance mechanisms acquired in a therapeutic setting. Common mechanisms of resistance were not involved in this resistance. Thus, we compared the gene expression profiles of sensitive, resistant, and reverted tumors using cDNA expression arrays. Expression of selected transcripts was confirmed by quantitative real-time PCR. We found that pleiotrophin (PTN), a heparin-binding growth factor, was the only gene significantly affected: PTN gene expression was downregulated in all resistant tumors (8-14-fold) as compared to sensitive tumors, and was increased (2-4-fold) in all reverted tumors as compared to resistant tumors. PTN thus appeared to be a likely candidate gene associated with resistance to CPT-11 in this in vivo model. To investigate the direct implication of PTN in NB, we transfected two NB cell lines with RNA interferences in order to silence PTN. PTN failed to demonstrate implication in resistance to CPT-11 in vitro but could influence sensitivity to CPT-11 exclusively through an in vivo mechanism. Indeed, vasculature was significantly enhanced in resistant NB xenografts compared to sensitive and reverted xenografts, and we suggest that PTN is acting in our resistant in vivo NB model as an angiostatic factor.

A phase I dose-finding clinical pharmacokinetic study of an oral formulation of irinotecan (CPT-11) administered for 5 days every 3 weeks in patients with advanced solid tumours

BACKGROUND

Oral administration of irinotecan (CPT-11) should allow sustained exposure to the drug without the inconvenience of intravenous delivery and with fewer side-effects.

PATIENTS AND METHODS

The present phase I trial of CPT-11, administered orally as a powder-filled capsule for 5 consecutive days every 3 weeks at doses ranging from 30 to 90 mg/m(2)/day, was conducted in 47 patients for whom a satisfactory standard treatment option was no longer available (24 males/23 females; median age 51 years, range 26-85). Tumour types included melanoma (11), colorectal (4), urinary tract (3), lung/pleura (4), thyroid (3), liver (3), gallbladder (2), cervix/uterus (3), breast (2), pancreas (2), carcinoma and other cancer types (10).

RESULTS

A total of 171 cycles were administered (median 3, range 1-11). Dose limiting toxicities (DLTs) occurred during the first cycle in five of 31 patients in the dose-escalation part of the study: one patient at the 50 mg/m(2)/day dose level (diarrhoea grade 4); one patient at the 80 mg/m(2)/day dose level (prolonged neutropenia grade 4 and diarrhoea grade 3); and three patients at the 90 mg/m(2)/day dose level (diarrhoea, vomiting and neutropenia). The 80 mg/m(2)/day dose level was expanded, as a feasibility study, to include 16 additional patients, five of whom had received extensive prior pelvic irradiation. A further three patients in this cohort experienced DLTs, two of whom had received extensive prior pelvic irradiation. One patient died on study day 15 during the first cycle of oral CPT-11 following grade 3 diarrhoea, febrile neutropenia and a necrotic enterocolitis. Overall the grade 3/4 toxicities in 47 patients were asthenia (19%), anorexia (17%), neutropenia (14.9 %), diarrhoea (13%), nausea (12.7%), vomiting (8.5%) and thrombocytopenia (8.5%). Partial responses were observed in two melanoma patients and disease stabilisation was noted in 17 (36.1%) patients. Pharmacokinetic parameters were recorded for 46 patients.

CONCLUSIONS

At the maximum tolerated dose, defined as 80 mg/m(2)/day for 5 days every 3 weeks, oral CPT-11 was shown to be well tolerated and safe with few of the haematological toxicities associated with the intravenous formulation.

Mammalian carboxylesterases: from drug targets to protein therapeutics

Our understanding of the detailed recognition and processing of clinically useful therapeutic agents has grown rapidly in recent years, and we are now able to begin to apply this knowledge to the rational treatment of disease. Mammalian carboxylesterases (CEs) are enzymes with broad substrate specificities that have key roles in the metabolism of a wide variety of clinical drugs, illicit narcotics and chemical nerve agents. Here, the functions, mechanism of action and structures of human CEs are reviewed, with the goal of understanding how these proteins are able to act in such a non-specific fashion, yet catalyze a remarkably specific chemical reaction. Current approaches to harness these enzymes as protein-based therapeutics for drug and chemical toxin clearance are described, as well as their uses for targeted chemotherapeutic prodrug activation. Also included is an outline of how selective CE inhibitors could be used as co-drugs to improve the efficacy of clinically approved agents.

Gefitinib enhances the antitumor activity and oral bioavailability of irinotecan in mice

As a single agent the ERBB1 inhibitor, gefitinib (Iressa; ZD1839) showed minimal activity against a panel of 10 pediatric tumor xenografts that do not express the ERBB1 receptor. However, combined with irinotecan (CPT-11), significantly greater than additive activity was observed in four of eight models (P < 0.05), and the combination showed enhanced activity against three additional tumor lines. Breast cancer resistance protein (ABCG2), a transporter that confers resistance to SN-38 (the active metabolite of irinotecan), was readily detected in six of nine xenograft models examined by immunohistochemistry. In vitro gefitinib potently reversed resistance to SN-38 only in a cell line that overexpressed functional ABCG2. However, overexpression of ABCG2 did not decrease accumulation nor increase the rate of efflux of [(14)C]gefitinib. On the basis of these results and the distribution of Abcg2 in mouse tissues, we assessed the ability of gefitinib to modulate irinotecan pharmacokinetics. Oral gefitinib coadministration resulted in no change in clearance of intravenously administered irinotecan. However, gefitinib treatment dramatically increased the oral bioavailability of irinotecan after simultaneous oral administration. It is concluded that gefitinib may modulate SN-38 activity at the cellular level to reverse tumor resistance mediated by ABCG2 through inhibiting drug efflux and may be used potentially in humans to modulate the oral bioavailability of a poorly absorbed camptothecin such as irinotecan.

No topoisomerase I alteration in a neuroblastoma model with in vivo acquired resistance to irinotecan

CPT-11 (irinotecan) is a DNA-topoisomerase I inhibitor with preclinical activity against neuroblastoma (NB) xenografts. The aim was to establish in vivo an NB xenograft resistant to CPT-11 in order to study the resistance mechanisms acquired in a therapeutic setting. IGR-NB8 is an immature NB xenograft with MYCN amplification and 1p deletion, which is sensitive to CPT-11. Athymic mice bearing advanced-stage subcutaneous tumours were treated with CPT-11 (27 mg kg⁻¹ day⁻¹ × 5) every 21 days (1 cycle) for a maximum of four cycles. After tumour regrowth, a new in vivo passage was performed and the CPT-11 treatment was repeated. After the third passage, a resistant xenograft was obtained (IGRNB8-R). The tumour growth delay (TGD) was reduced from 115 at passage 1 to 40 at passage 4 and no complete or partial regression was observed. After further exposure to the drug, up to 28 passages, the resistant xenograft was definitively established with a TGD from 17 at passage 28. Resistant tumours reverted to sensitive tumours after 15 passages without treatment. IGR-NB8-R remained sensitive to cyclophosphamide and cisplatin and cross-resistance was observed with the topoisomerase I inhibitor topotecan. No quantitative or qualitative topoisomerase I modifications were observed. The level of expression of multidrug resistance 1 (MDR1), MDR-associated protein 1 (MRP1) and, breast cancer resistance protein, three members of the ATP-binding cassette transporter family was not modified over passages. Our results suggest a novel resistance mechanism, probably not involving the mechanisms usually observed in vitro.

Phase I study of an oral formulation of irinotecan administered daily for 14�days every 3�weeks in patients with advanced solid tumours

A phase I study was conducted with oral irinotecan given daily for 14 days every 3 weeks in 45 patients with solid tumours to establish the maximum tolerated dose (MTD), toxicity, preliminary antitumour response and pharmacokinetics. Irinotecan was administered orally as a powder-filled capsule at doses ranging from 7.5 to 40 mg/m2 per day. Tumours were predominantly colorectal (30) together with 10 other gastrointestinal, 2 breast, 2 small cell lung and 1 ovarian. All but three patients had received prior chemotherapy. The median number of administered cycles was 3 (range 1-19). Gastrointestinal toxicities (grade 3 nausea, grade 3/4 vomiting and diarrhoea) and one incidence of grade 3 asthenia were dose limiting. There were no grade 3/4 haematological toxicities. The MTD was 30 mg/m2 per day. There were two documented partial responses, one in a patient with cancer of the small intestine and the other in a patient with colon cancer. Stable disease was seen in 16 patients (35.5%). Peak concentrations of irinotecan and metabolite SN-38 were reached within 2.0-2.4 h. The metabolic ratio of SN-38 AUC to irinotecan AUC was 0.17+/-0.10 (mean+/-SD). The dose recommended for phase II studies is 30 mg/m2 per day administered daily for 14 days every 3 weeks.

Discovery of Novel Selective Inhibitors of Human Intestinal Carboxylesterase for the Amelioration of Irinotecan-Induced Diarrhea: Synthesis, Quantitative Structure-Activity Relationship Analysis, and Biological Activity

The dose-limiting toxicity of the highly effective anticancer agent 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothecin (irinotecan; CPT-11) is delayed diarrhea. This is thought to be caused by either bacteria-mediated hydrolysis of the glucuronide conjugate of the active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38) or direct conversion of CPT-11 to SN-38 by carboxylesterases (CE) in the small intestine. After drug administration, a very high level of CPT-11 is present in the bile; this is deposited into the duodenum, the region of the gut with the highest levels of CE activity. Hence, it is likely that direct conversion of the drug to SN-38 is partially responsible for the diarrhea associated with this agent. In an attempt to ameliorate this toxicity, we have applied Target-Related Affinity Profiling to identify novel CE inhibitors that are selective inhibitors of the human intestinal enzyme (hiCE). Seven inhibitors, all sulfonamide derivatives, demonstrated greater than 200-fold selectivity for hiCE compared with the human liver CE hCE1, and none was an inhibitor of human acetylcholinesterase or butyrylcholinesterase. Quantitative structure-activity relationship (QSAR) analysis demonstrated excellent correlations with the predicted versus experimental Ki values (r2 = 0.944) for hiCE. Additionally, design and synthesis of a tetrafluorine-substituted sulfonamide analog, which QSAR indicated would demonstrate improved inhibition of hiCE, validated the computer predictive analyses. These and other phenyl-substituted sulfonamides compounds are regarded as lead compounds for the development of effective, selective CE inhibitors for clinical applications.

In Vivo Treatment with CPT-11 Leads to Differentiation of Neuroblastoma Xenografts and Topoisomerase I Alterations

Topoisomerase I inhibitors, such as CPT-11, are potent anticancer drugs against neuroblastoma (NB). Differentiating agents, such as retinoids, improve the survival of children with metastatic NB. To characterize the biological effects associated with exposure to CPT-11 in vivo, athymic mice bearing a human NB xenograft, named IGR-NB8 and characterized as an immature NB with poor prognostic markers, were treated with CPT-11. Prolonged stable disease was observed, resulting in an overall tumor growth delay of 115 days. During treatment, tumors differentiated into ganglioneuroblastomas (GGNB), which reverted into an immature phenotype when treatment was discontinued. In contrast, 13-cis retinoic acid failed to induce differentiation of IGR-NB8 in vivo. Tumor differentiation was associated with decreased N-myc expression, induction of p73 expression in the perinuclear area and cytoplasm, and a dramatic 35-fold decrease in topoisomerase I (topo I) catalytic activity. The full-length Mr 100,000 topo I protein was present in both pre and post-treatment immature NB xenografts. In contrast, differentiated GGNBs did not contain the Mr 100,000 protein but an intense Mr 48,000 topo I fragment. Furthermore, redistribution of the Mr 48,000 and 68,000 forms to the cytoplasm was observed in differentiated tumors. The same pattern of topo I expression and catalytic activity was observed in NBs and GGNBs obtained from pediatric patients. Our data suggest that prolonged in vivo exposure to CPT-11 induces differentiation of NB xenografts, which is associated with truncation of the topo I enzyme, relocation of the degraded forms to the cytoplasm, and decreased catalytic activity.

The importance of tumor glucuronidase in the activation of irinotecan in a mouse xenograft model

The anticancer drug irinotecan (CPT-11) is activated to the potent topoisomerase I inhibitor, SN-38 (7-ethyl-10-hydroxycamptothecin), by esterases. SN-38 is in turn conjugated to the inactive SN-38 glucuronide (SN-38G). The reverse reaction is mediated by beta-glucuronidases. Hence, production of SN-38 may occur through either pathway. In this study we conducted in vitro studies to examine these two reactions in neuroblastoma xenograft tumors (NB1691) and compared the rates of SN-38 production with those observed in the liver and plasma of the host SCID (severe-combined immunodeficient) mice. The rate of formation of SN-38 from CPT-11 by esterases slowed considerably during a 60-min incubation, consistent with the known deacylation-limited nature of this reaction. For xenograft tumor tissue, K(m) and V(max) values of 1.6 microM and 4.4 pmol/min/mg of protein, respectively, were observed. By comparison, these parameters were estimated to be 6.9 microM and 9.4 pmol/min/mg for mouse liver and 2.1 microM and 40.0 pmol/min/mg for mouse plasma, respectively. The formation of SN-38 from SN-38G was very pronounced in both liver and xenograft tumor tissue, in which it was nonsaturable (0.125-50 microM) and time-independent (0-60 min). The derived values of V(max)/K(m) were 0.65 microl/min/mg for the tumor and 2.12 microl/min/mg for the liver preparations. Microdialysate experiments revealed the concentrations of SN-38G and CPT-11 in tumor to be comparable. At equal substrate concentrations, production of SN-38 from SN-38G in tumor extracts was comparable with that from CPT-11. Therefore, reactivation of SN-38 in the tumor by beta-glucuronidases may represent an important route of tumor drug activation for CPT-11.

Secreted and tumour targeted human carboxylesterase for activation of irinotecan

Irinotecan (CPT-11) is an anticancer agent for the treatment of colon cancer. CPT-11 can be considered as a prodrug, since it needs to be activated into the toxic drug SN-38 by the enzyme carboxylesterase. An approach to achieve tumour specific activation of CPT-11 is to transduce the cDNA encoding carboxylesterase into tumour cells. A secreted form of carboxylesterase may diffuse through a tumour mass and may activate CPT-11 extracellularly. This could enhance the antitumour efficacy by exerting a bystander effect on untransduced cells. In addition a secreted tumour-targeted form of carboxylesterase should prevent leakage of the enzyme from the site of the tumour into the circulation. We have constructed a secreted form of human liver carboxylesterase-2 by deletion of the cellular retention signal and by cloning the cDNA downstream of an Ig kappa leader sequence. The protein was secreted by transfected cells and showed both enzyme activity and efficient CPT-11 activation. To obtain a secreted, tumour-targeted form of carboxylesterase-2 the cDNA encoding the human scFv antibody C28 directed against the epithelial cell adhesion molecule EpCAM, was inserted between the leader sequence and carboxylesterase-2. This fusion protein showed CPT-11 activation and specific binding to EpCAM expressing cells. Importantly, in combination with CPT-11 both recombinant carboxylesterase proteins exerted strong antiproliferative effects on human colon cancer cells. They are, therefore, promising new tools for gene directed enzyme prodrug therapy approaches for the treatment of colon carcinoma with CPT-11.

Structural constraints affect the metabolism of 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) by carboxylesterases

7-Ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin [CPT-11 (irinotecan)] is a water-soluble camptothecin-derived prodrug that is activated by esterases to yield the potent topoisomerase I poison SN-38. We identified a rabbit liver carboxylesterase (CE) that was very efficient at CPT-11 metabolism; however, a human homolog that was more than 81% identical to this protein activated the drug poorly. Recently, two other human CEs have been isolated that are efficient in the conversion of CPT-11 to SN-38, yet both demonstrate little homology to the rabbit protein. To understand this phenomenon, we have characterized a series of esterases from human and rabbit, including several chimeric proteins, for their ability to metabolize CPT-11. Computer predictive modeling indicated that the ability of each enzyme to activate CPT-11 was dependent on the size of the entrance to the active site. Kinetic studies with a series of nitrophenyl and naphthyl esters confirmed these predictions, indicating that activation of CPT-11 by a CE is constrained by size-limited access of the drug to the active site catalytic amino acid residues.

Synthesis and biological evaluation of novel A-ring modified hexacyclic camptothecin analogues

Eleven A-ring modified hexacyclic analogues of camptothecin (CPT) containing a 1,4-oxazine ring were synthesized from 10-hydroxycamptothecin (11a) and 7-ethyl-10-hydroxycamptothecin (3) (SN-38) in four to five steps and were subjected to the biological tests such as cytotoxicity, topoisomerase I (Topo I) inhibitory activity, acetylcholinesterase (AChE) inhibition, and stability in human plasma. Four compounds 15a, 15b, 16a, and 16c were about 2-fold more potent than topotecan and as potent as CPT toward human cancer cell lines A549, H128, WiDr, MKN45, SK-OV-3, and SK-BR-3 in vitro, even though the most active compound 15b was slightly less potent than SN-38. The potency of Topo I inhibition of these compounds showed relatively good correlation with their cytotoxicity. Most of the compounds exhibited AChE inhibitory activity weaker (9 +/- 2 to 20 +/- 3%) than CPT (23 +/- 5%) or topotecan (20 +/- 4%) and similar to SN-38 (13 +/- 2%), indicating that they might have little effect on causing early diarrhea. The stability of lactone forms of these compounds in human plasma seemed to be much higher than that of CPT and similar to that of topotecan but lower than that of SN-38. Among the new hexacyclic CPT analogues, compound 15b showed higher antitumor activity against human tumor xenograft, WiDr, in nude mice compared to that of SN-38. The most promising compound 15b has been selected for further development.

Modulation of camptothecin analogs in the treatment of cancer: a review

The topoisomerase I inhibitors reviewed in this paper are all semisynthetic analogs of camptothecin (CPT). Modulation of this intranuclear enzyme translates clinically in to antitumor activity against a broad spectrum of tumors and is therefore the subject of numerous investigations. We present preclinical and clinical data on CPT analogs that are already being used in clinical practice [i.e. topotecan and irinotecan (CPT-11)] or are currently in clinical development (e.g. 9-aminocamptothecin, 9-nitrocamptotecin, lurtotecan, DX 8951f and BN 80915), as well as drugs that are still only developed in a preclinical setting (silatecans, polymer-bound derivates). A variety of different strategies is being used to modulate the systemic delivery of this class of agents, frequently in order to increase antitumor activity and/or reduce experienced side effects. Three principal approaches are discussed, including: (i) pharmaceutical modulation of formulation vehicles, structural alterations and the search for more water-soluble prodrugs, (ii) modulation of routes of administration and considerations on infusion duration, and (iii) both pharmacodynamic and pharmacokinetic biomodulation.

Direct translation of a protracted irinotecan schedule from a xenograft model to a phase I trial in children

PURPOSE

In a preclinical model of neuroblastoma, administration of irinotecan daily 5 days per week for 2 consecutive weeks ([qd x 5] x 2) resulted in greater antitumor activity than did a single 5-day course with the same total dose. We evaluated this protracted schedule in children.

PATIENTS AND METHODS

Twenty-three children with refractory solid tumors were enrolled onto a phase I study. Cohorts received irinotecan by 1-hour intravenous infusion at 20, 24, or 29 mg/m(2) (qd x 5) x 2 every 21 days.

RESULTS

The 23 children (median age, 14.1 years; median prior regimens, two) received 84 courses. Predominant diagnoses were neuroblastoma (n = 5), osteosarcoma (n = 5), and rhabdomyosarcoma (n = 4). The dose-limiting toxicity was grade 3/4 diarrhea and/or abdominal cramps in six of 12 patients treated at 24 mg/m(2), despite aggressive use of loperamide. The maximum-tolerated dose (MTD) on this schedule was 20 mg/m(2)/d. Five patients had partial responses and 16 had disease stabilization. On day 1, the median systemic exposure to SN-38 (the active metabolite of irinotecan) at the MTD was 106 ng-h/mL (range, 41 to 421 ng-h/mL).

CONCLUSION

This protracted schedule is well tolerated in children. The absence of significant myelosuppression and encouraging clinical responses suggest compellingly that irinotecan be further evaluated in children using the (qd x 5) x 2 schedule, beginning at a dose of 20 mg/m(2). These results imply that data obtained from xenograft models can be effectively integrated into the design of clinical trials.

Phase I and pharmacokinetic trial of oral irinotecan administered daily for 5 days every 3 weeks in patients with solid tumors

PURPOSE

We conducted a phase I dose-escalation trial of orally administered irinotecan (CPT-11) to characterize the maximum-tolerated dose (MTD), dose-limiting toxicities (DLTs), pharmacokinetic profile, and antitumor effects in patients with refractory malignancies.

PATIENTS AND METHODS

CPT-11 solution for intravenous (IV) use was mixed with CranGrape juice (Ocean Spray, Lakeville-Middleboro, MA) and administered orally once per day for 5 days every 3 weeks to 28 patients. Starting dosages ranged from 20 to 100 mg/m2/d.

RESULTS

Grade 4 delayed diarrhea was the DLT at the 80 mg/m2/d dosage in patients younger than 65 years of age and at the 66 mg/m2/d dosage in patients 65 or older. The other most clinically significant toxicity of oral CPT-11 was neutropenia. A linear relationship was found between dose, peak plasma concentration, and area under the concentration-time curve (AUC) for both CPT-11 and SN-38 lactone, implying no saturation in the conversion of irinotecan to SN-38. The mean metabolic ratio ([AUC(SN-38 total) + AUC(SN-38G total)]/AUC(CPT-11 total)) was 0.7 to 0.8, which suggests that oral dosing results in presystemic conversion of CPT-11 to SN-38. An average of 72% of SN-38 was maintained in the lactone form during the first 24 hours after drug administration. One patient with previously treated colorectal cancer and liver metastases who received oral CPT-11 at the 80 mg/m2/d dosage achieved a confirmed partial response.

CONCLUSION

The MTD and recommended phase II dosage for oral CPT-11 is 66 mg/m2/d in patients younger than 65 years of age and 50 mg/m2/d in patients 65 or older, administered daily for 5 days every 3 weeks. The DLT of diarrhea is similar to that observed with IV administration of CPT-11. The biologic activity and favorable pharmacokinetic characteristics make oral administration of CPT-11 an attractive option for further clinical development.

Animal models for studying the action of topoisomerase I targeted drugs

Almost 30 years after the unsuccessful clinical evaluation of camptothecin sodium, there has been a revival in interest in this class of agent that poisons topoisomerase I. Currently there are four camptothecin analogues in clinical trials each at different levels of advancement. Clinical data suggest that patterns of antitumor activity and toxicity profiles differ between analogues. In preclinical models antitumor activity appears to be highly schedule-dependent. Here we review rodent and human tumor models used in evaluation of efficacy, and models used to predict toxicities of these compounds. The major limitation of rodent models is that the mouse tolerates significantly greater systemic exposure to each camptothecin analogue than do patients. This leads to a false overprediction of potential clinical activity. However, responses of human tumor xenografts in mice are highly predictive of responses of clinical cancer when camptothecins are administered at dose levels achieving similar systemic exposure in mice. Development of assays that identify analogues that maintain therapeutic activity in mice, but have less species differential toxicity, particularly to the hematopoietic system, may provide an early screen to select compounds having greater clinical utility.

Preclinical development of camptothecin derivatives and clinical trials in pediatric oncology

Although the prognosis of childhood cancers has dramatically improved over the last three decades, new active drugs are needed. Camptothecins represent a very attractive new class of anticancer drugs to develop in paediatric oncology. The preclinical and clinical development of two of these DNA-topoisomerase I inhibitors, i.e. topotecan and irinotecan, is ongoing in paediatric malignancies. Here we review the currently available results of this evaluation. Topotecan proved to be active against several paediatric tumour xenografts. In paediatric phase I studies exploring several administration schedules, myelosuppression was dose-limiting. The preliminary results of topotecan evaluation in phase II study showed antitumour activity in neuroblastoma (response rate: 15% at relapse and 37% in newly diagnosed patients with disseminated disease) and in metastatic rhabdomyosarcoma (40% in untreated patients). Topotecan-containing drug combinations are currently investigated. Irinotecan displayed a broad spectrum of activity in paediatric solid tumour xenografts, including rhabdo-myosarcoma, neuroblastoma, peripheral primitive neuroectodermal tumour, medulloblastoma, ependymoma, malignant glioma and juvenile colon cancer. For several of these histology types, tumour-free survivors have been observed among animals bearing an advanced-stage tumour at time of treatment. The clinical evaluation of irinotecan in children is ongoing. Irinotecan undergoes a complex in vivo biotransformation involving several enzyme systems, such as carboxylesterase, UDPGT and cytochrome P450, in children as well as in adults. Preclinical studies of both drugs have shown that their activity was schedule-dependent. The optimal schedule of administration is an issue that needs to be addressed in children. In conclusion, the preliminary results of the paediatric evaluation of camptothecin derivatives show very encouraging results in childhood malignancies. The potential place of camptothecins in the treatment of paediatric malignant tumours is discussed.

Oral versus intraperitoneal administration of irinotecan in the treatment of human neuroblastoma in nude mice

The present study evaluated the plasma pharmacokinetics of irinotecan (CPT-11) and its effects against a human neuroblastoma in xenograft, given by different administration routes. One-third of the LD50 was administered either intraperitoneally (59 mg/kg mouse weight (MW)) or orally (404 mg/kg MW) to nude mice. The plasma levels of CPT-11 and its active metabolite SN-38 decreased rapidly when CPT-11 was administered intraperitoneally, but remained relatively high for 4-8 h after oral administration. Then, a human neuroblastoma xenograft was inoculated in another set of 21 nude mice. When the estimated tumor weight reached 150-200 mg, CPT-11 was administered in the total LD50 either intraperitoneally or orally in three doses at 4-day intervals (q4d x3) to the mice in each experimental group. Oral administration was found to be superior to intraperitoneal injection in terms of tumor inhibition and to be an effective route for CPT-11 administration in the treatment of human neuroblastoma in nude mice.